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Abstract

Gale (1978) reported the combined solvent power of supercritical fluids with the solvent power of micellar solutions which appears promising in connection with enhanced oil recovery. Likewise, recognition of the possible formation and destruction of reversed micellar by possible formation and destruction of reversed micellar by naturally-occurring amphiphilic substances, such as those associated with asphaltenes, may explain problems experienced in some EOR projects. Lipophilic supercritical components of reservoir fluids (e.g. light hydrocarbons and CO2) interact, in a controllable manner, with hydrophilic micellar complexes to achieve selective extraction of desirable components of crude oil. Fundamentals of supercritical fluids and of micellar systems are reviewed in terms of their mutual interaction and their potential applicability in EOR processes. potential applicability in EOR processes

Introduction

Phenomena associated with reversed micelles in supercritical Phenomena associated with reversed micelles in supercritical fluid-surfactant solutions (Gale et al., 1987; Blitz et al, 1988; Fulton and Smith 1988a and 1988b; and Fulton et al, 1989; Kaler et al, 1991; Tingey et al, 1991; Yee et al, 1991) seem relevant to resin-asphaltene phenomena in reservoir fluids. There appear to be common forms of phenomena in reservoir fluids. There appear to be common forms of interaction involving (1) apolar (polar) supercritical fluid, (2) amphiphilic substances, and (3) practically insoluble polar (apolar) material. it is the purpose of this presentation to highlight the phenomenon with respect to its probable significance in petroleum phenomenon with respect to its probable significance in petroleum production and reservoir behavior. Table 1 illustrates comparison between production and reservoir behavior. Table 1 illustrates comparison between related manifestations of this phenomena.

In petroleum reservoirs, naturally-occurring light ends are the supercritical fluid, resins and associated organic acids are natural surfactants, and low-solubility polar materials such as asphaltenes are the core of reversed micelles.

Most investigations of reversed micelle phenomena in supercritical fluid-surfactant solutions have focussed on non-petroleum applications, e.g. the extraction of enzymes (Rao et al, 1990; Dekker et al, 1991), proteins (Phillips, 1991), and amino acids (Lement et al, 1990). proteins (Phillips, 1991), and amino acids (Lement et al, 1990). EOR applications of reversed micelles have been previously discussed (Langevin, 1984; Neogi, 1987; Fulton and Smith, 1988a); however, there have been essentially no reported studies of reversed micelles in supercritical fluid-surfactant solutions in petroleum reservoirs or in petroleum reservoir model systems. Specifically, resin-asphaltene petroleum reservoir model systems. Specifically, resin-asphaltene phenomena (Hall and Herron, 1981; Heithaus, 1962) have not been phenomena (Hall and Herron, 1981; Heithaus, 1962) have not been investigated in terms of their potential for EOR and/or naturally-occurring reversed micelle behavior.

There are two categories of reversed micelle phenomena in petroleum reservoir operations. In the first category, surfactants are added to a reservoir to form a viscous micellar fluid interface between the reservoir fluid and the injected fluid, to inhibit viscous fingering and/or gravity override in enhanced oil recovery. in the second category, natural surfactants, present in the reservoir fluid itself, interact with injected supercritical fluids (e.g. carbon dioxide or light hydrocarbons) and/or with supercritical components of the reservoir fluid, and with asphaltenes to form reversed micelles having increased mobility in the crude oil system. Pressure change, associated with flow of reservoir fluid in porous media results in a corresponding change in solvent power of the supercritical fluid, rupturing the reversed micelles and depositing insoluble micellar core material within the reservoir.

Enhanced oil recovery projects have introduced supercritical CO2, dry gas or rich gas into partially-depleted petroleum reservoirs. in some cases, EOR results have been favorable, while in other cases, results have been discouraging (Orr et al, 1981; Orr and Taber, 1984; Monger and Trujillo, 1991; Christman and Gorrell, 1990). Surfactants used in EOR operations are usually selected in order to reduce surface tension between the bulk reservoir fluid and the formation, and/or to form a viscous emulsion which stabilizes the displacement front between the injected fluid and the reservoir fluid. These surfactants need to be evaluated with regard to the potential formation of reversed micelles through interaction with the potential formation of reversed micelles through interaction with the reservoir fluid.

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